You can’t create a REST API only with html. A REST API means that you defines a “resource” and you utilize the HTTP (usually) protocol in order to change the “state” of the resource. For example: the resource is http://example.com/a. You can make a GET request in order to get this resource, POST for changing it and DELETE for deleting it.
As you can see, it’s a work with the server and not with the content that the client sees (html) – You need a server-side language, like: Python, Java, Php, etc.
Please tell us if you know a server-side language and we will be able to tell you how you can program a REST API in that language.
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solved Redmine REST API -client-server [closed]